Patent application WO 2011/009 560 describes stable aqueous dispersions containing core/shell two-phase structured particles with a hard core P1 with a Tg1 from 60 to 120° C. and a soft shell P2 with a Tg2 from −20 to 40° C. and an MFT from 0 to 50° C. with P1 representing from 15% to 60% out of P1+P2 for applications in aqueous coatings, which are in particular self-crosslinkable. Despite the very good capacity for film formation and the control of this process with good reproducibility of the film formation and of the performance, these dispersions require the use of monomers bearing functions that are crosslinkable in post-crosslinking, either by self-crosslinking or by adding external crosslinking agents, to achieve the performance levels demanded by the market, in particular:                in terms of resistance to wet abrasion in highly charged interior wall paints, i.e. VPC higher than the critical VPC (VPC: volume-based pigment concentration) for which the binder must be capable of interacting strongly with the pigments and fillers, with good wetting of said pigments and fillers        in terms of durability and water resistance in moderately charged exterior wall paints (VPC close to or less than the critical VPC) which are not self-crosslinkable, in contrast with the prior art.        
Other solutions exist for applications of this type, but they make use of non-structured particles of low MFT (below 5° C.). If they are not crosslinkable, as explained above, the resistance to soiling is poor.
To overcome the drawbacks of the prior art, it is proposed, according to the present invention, to modify a structured dispersion of the prior art (WO 2011/009 560) already involving a hard core phase P1 and a soft shell phase P2 by adding a second specific phase shell P3 of controlled molecular mass and with a Tg3 ranging from Tg2−5° C. to Tg2+5° C. and preferably Tg3 being equal to Tg2±2° C., with the additional soft phase P3 of lower mass than P2 being added in addition to the soft shell P2 (enveloping P2) in a specific content.
Thus, the hard/soft/soft P1/P2/P3 solution of the present invention makes it possible readily to achieve the targeted performance qualities mentioned, i.e. high resistance to soiling and to wet abrasion, without using crosslinkable systems and without losing the performance qualities that are inherent in the starting structure (P1/P2) thus modified and having ease of implementation and perfect reproducibility of the structure of the film formation and of the performance qualities. The present invention thus seeks to develop a stable dispersion, of controlled MFT, for the formulation of aqueous coatings with good resistance to soiling and to wet abrasion.